The present invention relates to a siloxane-based resin and a method for forming insulating film between interconnect layers in semiconductor devices by using the same. More specifically, the present invention relates to a siloxane-based resin prepared by hydrolyzing and polycondensing cyclic and/or cage-shape siloxane compounds, optionally with at least one silane compound, in an organic solvent in the presence of a catalyst and water. The present invention also relates to a method for forming insulating film between interconnect layers in semiconductor devices, wherein the siloxane-based resin described above is used as low dielectric insulating materials.
As the circuit density in multilevel integrated circuit devices increases, the reduction of feature size in a semiconductor device is strongly required. But, there are fatal problems such as R(resistance)xc3x97C(capacitance) delay due to crosstalk between interconnect lines. Therefore, dielectric constant of interlayer insulating films should be lowered so as to decrease the RC delay as much as possible. For this purpose, there have been various attempts to develop low dielectric materials for use in the insulating film.
For example, polysilsesquioxanes having dielectric constant of approximately 2.5xcx9c3.1 has replaced SiO2 having dielectric constant of 4.0 in chemical vapor deposition(CVD). Such polysilsesquioxanes can be also applied to a spin coating method due to its excellent planation property.
The polysilsesquioxanes as well as preparing methods thereof are well known in the art. For example, U.S. Pat. No. 3,615,272 discloses a method for preparing completely condensed soluble hydrogensilsesquioxane resins, which comprises the steps of condensing trichlorosilanes in a sulfuric acid medium, and then washing the resulting resins with water or aqueous sulfuric acid. U.S. Pat. No. 5,010,159 discloses a method for synthesizing soluble condensed hydridosilicon resins, which comprises the steps of hydrolyzing hydridosilanes in an arylsulfuric acid hydrate-containing hydrolysis medium, and then contacting the resulting resins with a neutralizing agent. U.S. Pat. No. 6,232,424 describes a highly soluble silicone resin composition having excellent solution stability, which was prepared by hydrolyzing and polycondensing tetraalkoxysilane, organosilane and organotrialkoxysilane monomers in the presence of water and a catalyst. U.S. Pat. No. 6,000,339 teaches that a silica-based compound, which may be useful for improving the resistance and physical properties as well as thickness of a coating film, can be obtained from a reaction of a monomer selected from the group consisting of alkoxysilane, fluorine-containing alkoxysilane and alkylalkoxysilane and a titanium- or zirconium-alkoxide compound in the presence of water and a catalyst. U.S. Pat. No. 5,853,808 describes that silsesquioxane polymers that are useful for preparing SiO2-rich ceramic coatings can be obtained as the polymeric reaction products from the hydrolysis and condensation of organosilanes having a xcex2-substituted alkyl group.
However, the prior polysilsesquioxane resins have not accomplished very low dielectric constant that is currently required for insulating film between interconnect layers in semiconductor devices. Additionally, they have been required to improve in mechanical properties, thermal stability, crack-resistance, and so on.
A feature of the present invention is a method for forming low dielectric insulating film between interconnect layers in semiconductor devices by using a siloxane-based resin having very low dielectric constant, wherein the resin is obtained from the copolymerization of cyclic and/or cage-shape siloxane compounds optionally with one or more silane compounds.
An aspect of the present invention relates to siloxane-based resins that are prepared by hydrolyzing and polycondensing a cyclic siloxane compound of formula (1) and a cage-shape siloxane compound of any of formulas (2a)-(2c) in an organic solvent in the presence of a catalyst and water: 
wherein,
R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl;
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo;
p is an integer from 3 to 8; and
m is an integer from 1 to 10; 
xe2x80x83in the above formulas (2a)-(2c),
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo,
provided that at least one is alkoxy or halo; and
n is an integer from 1 to 12.
Another aspect of the present invention relates to siloxane-based resins that are prepared by hydrolyzing and polycondensing a cyclic siloxane compound of formula (1) and a cage-shape siloxane compound of any of formulas (2a)-(2c), together with a silane compound of formula (3) and/or a silane compound of formula (4), in an organic solvent in the presence of a catalyst and water: 
wherein,
R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl;
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo;
p is an integer from 3 to 8; and
m is an integer from 1 to 10; 
xe2x80x83in the above formulas 2(a)-2(c),
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo; and
n is an integer from 1 to 12;
SiX1X2X3X4xe2x80x83xe2x80x83(3)
xe2x80x83wherein,
each of X1, X2, X3, and X4 is, independently, C1-10 alkoxy, or halo;
RSiX1X2X3xe2x80x83xe2x80x83(4)
xe2x80x83wherein,
R is H, C1-3 alky, C3-10 cycloalkyl, or C6-15 aryl; and
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo.
Still another aspect of the present invention relates to siloxane-based resins that are prepared by hydrolyzing and polycondensing a cyclic siloxane compound of formula (1), together with a silane compound of formula (3) and/or a silane compound of formula (4), in an organic solvent in the presence of a catalyst and water: 
wherein,
R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl;
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo;
p is an integer from 3 to 8; and
m is an integer from 1 to 10;
SiX1X2X3X4xe2x80x83xe2x80x83(3)
xe2x80x83wherein,
each of X1, X2, X3, and X4 is, independently, C1-10 alkoxy, or halo;
RSiX1X2X3xe2x80x83xe2x80x83(4)
xe2x80x83wherein,
R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl; and
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo.
Still another aspect of the present invention relates to siloxane-based resins that are prepared by hydrolyzing and polycondensing a cage-shape siloxane compound of any of formulas (2a)-(2c), together with a silane compound of formula (3) and/or a silane compound of formula (4), in an organic solvent in the presence of a catalyst and water: 
in the above formulas (2a)-(2c),
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo; and
n is an integer from 1 to 12;
SiX1X2X3X4xe2x80x83xe2x80x83(3)
xe2x80x83wherein,
each of X1, X2, X3, and X4 is, independently, C1-10 alkoxy, or halo;
RSiX1X2X3xe2x80x83xe2x80x83(4)
xe2x80x83wherein,
R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl; and
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo.
Still another aspect of the present invention relates to a method for forming insulating film between interconnect layers in semiconductor devices, the method comprising the steps of: providing a resinous solution by dissolving the siloxane-based resin described above in an organic solvent; coating a silicon wafer with the resinous solution; and heat-curing the resulting coating film.
All of the above features and other features of the present invention will be successfully achieved from the present invention described in the following.
The Priority Korean Patent Application Nos. 2001-15884 filed on Mar. 27, 2001 and 2001-56798 filed on Sep. 14, 2001 are hereby incorporated in their entirety by reference.
A siloxane-based resin of the present invention is prepared by hydrolyzing and polycondensing cyclic and/or cage-shape siloxane monomers, optionally with at least one silane monomer, in an organic solvent in the presence of a catalyst and water.
The cyclic siloxane monomers used in the present invention can be represented by the following formula (1): 
wherein,
R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl;
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo;
p is an integer from 3 to 8; and
m is an integer from 1 to 10.
As can be seen from the above formula (1), two silicon atoms are linked to each other through an oxygen atom to form cyclic structure, and the terminal of each branch comprises at least one hydrolysable group. These cyclic siloxane monomers, for example, may be obtained from a hydrosililation reaction using a metal catalyst.
The cage-shape siloxane monomers used in the present invention can be represented by one of the following formulas (2a)-(2c): 
in the above formulas (2a)-(2c),
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo; and
n is an integer from 1 to 12.
As can be seen from the above formulas (2a)-(2c), two silicon atoms are linked to each other through an oxygen atom to form cyclic structure, and the terminal of each branch comprises at least one hydrolysable group.
As the cage-shape siloxane monomers, commercially available ones whose terminal functional groups are halogens can be used, without modification or after substitution of the terminal halogens with alkyl and/or alkoxy groups. Such substitution may be accomplished by any of standard methods well known in the art. For example, the substitution of the terminal halogens with alkoxy groups can be readily accomplished through reacting the halogenated cage-shape siloxane compound with an alcohol and a triethylamine.
On the other hand, the silane monomers used in the present invention can be represented by the following formula (3), in which Si has four hydrolysable substituents:
SiX1X2X3X4xe2x80x83xe2x80x83(3)
wherein,
each of X1, X2, X3, and X4 is, independently, C1-10 alkoxy, or halo.
Non-limiting examples of such silane monomer include tetra-n-butoxysilane, tetra-n-propoxysilane, tetraethoxysilane, tetramethoxysilane, tetrachlorosilane, tetrabromosilane, tetrafluorosilane, triethoxychlorosilane, and trimethoxychlorosilane.
Also, the other silane monomers represented by the following formula (4) can be used in the preparation of the siloxane-based resins of the present invention, in which Si has at least one hydrolysable substituent:
RSiX1X2X3xe2x80x83xe2x80x83(4)
wherein,
R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl; and
each of X1, X2, and X3 is, independently, C1-3 alkyl, C1-10 alkoxy, or halo, provided that at least one is alkoxy or halo.
Non-limiting examples of such silane monomer include methyltriethoxysilane, methyltrimethoxysilane, methyltri-n-propoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltrichlorosilane, phenyltrifluorosilane, methyltrichlorosilane, methyltribromosilane, methyltrifluorosilane, triethoxysilane, trimethoxysilane, trichlorosilane, and trifluorosilane.
The siloxane-based resins of the present invention can be obtained as copolymeric products from the hydrolysis and polycondensation of the cyclic siloxane compound of formula (1)(hereinafter, referred to as siloxane compound (1)) and the cage-shape siloxane compound of formula (2) (hereinafter, referred to as siloxane compound (2)) in an organic solvent in the presence of a catalyst and water. Alternatively, the siloxane-based resins of the present invention can be prepared by hydrolyzing and polycondensing either or both of siloxane compounds (1) and (2), together with either or both of the silane compound of formula (3)(hereinafter, referred to as silane compound (3)) and the silane compound of formula (4) (hereinafter, referred to as silane compound (4)), in an organic solvent in the presence of a catalyst and water.
For the preparation of a binary copolymer from siloxane compounds (1) and (2), the molar ratio of compound (1) vs. compound (2) is between 0.1:99.9 and 99.9:0.1, preferably 5:95 and 50:50.
On the other hand, for the preparation of a ternary copolymer from both siloxane compounds (1) and (2), in conjunction with either silane compound (3) or (4), an amount of each compound ranges from 1 to 98 mol %, respectively.
Moreover, a quaternary copolymer can be prepared by using both silane compounds (3) and (4) in conjunction with both siloxane compounds (1) and (2). At this time, each of the four compounds is used in an amount of 1-97 mol %, respectively.
In the present invention, as siloxane monomers, both cyclic and cage-shape siloxane compounds are not always used in combination, and thus it is also possible to use either of the cyclic and cage-shape siloxane compounds.
Where cyclic siloxane compound (1) is solely used as a siloxane monomer, silane compound (3) is preferably copolymerized therewith to provide a binary copolymer, wherein the molar ratio of compound (1) vs. compound (3) is between 99.9:0.1 and 0.1:99.9, preferably 95:5 and 50:50. Alternatively, silane compound (4) can be additionally employed in the copolymerization to provide a ternary copolymer. This ternary copolymer contains 1-98 mol % of compound (1), 1-98 mol % of compound (3), and 1-98 mol % of compound (4).
Similarly, where cage-shape siloxane compound (2) is solely used as a siloxane monomer, silane compound (4) is preferably copolymerized therewith to provide a binary copolymer, wherein the molar ratio of compound (2) vs. compound (4) is between 0.1:99.9 and 99.9:0.1, preferably 5:95 and 50:50. Alternatively, silane compound (3) can be further added to the copolymerization reaction to provide a ternary copolymer. This ternary copolymer contains 1-98 mol % of compound (2), 1-98 mol % of compound (3), and 1-98 mol % of compound (4).
As the organic solvents used in the preparation of the siloxane-based resins according to the present invention, aromatic hydrocarbon solvent, aliphatic hydrocarbon solvent, ketone-based solvent, ether-based solvent, acetate-based solvent, alcohol-based solvent, silicon-based solvent, or mixtures thereof are preferred.
Exemplary catalysts used in the present invention include, without limitation, hydrochloric acid, nitric acid, benzene sulfonic acid, oxalic acid, formic acid, potassium hydroxide, sodium hydroxide, triethylamine, sodium bicarbonate, pyridine, and mixtures thereof.
In the hydrolysis and polycondensation reaction according to the present invention, the molar ratio of the catalyst vs. monomers to be polymerized(inclusive of siloxane and silane compounds) is preferably between 0.00001:1 and 10:1. Further, 0.1-1,000 mol of water is added to 1 mol of the monomers. Then, the hydrolysis and polycondensation are carried out at a temperature of 0-200xc2x0 C., preferably 50-110xc2x0 C., for 0.1-100 hrs, preferably 3-48 hrs.
The siloxane-based resins thus prepared have Mw of 3,000 to 500,000, preferably 3,000 to 100,000. Preferably, Sixe2x80x94OR content in the whole terminal groups represented by Sixe2x80x94OR and/or Sixe2x80x94R is more than 5 mol %, wherein R is H, C1-3 alkyl, C3-10 cycloalkyl, or C6-15 aryl. The siloxane-based resins of the present invention can be used as matrix precursors of insulating film between interconnect layers in semiconductor devices.
Particular method for forming insulating film between interconnect layers in semiconductor devices by using the siloxane-based resins according to the present invention is described below.
As mentioned above, a method for forming insulating film between interconnect layers in semiconductor devices of the present invention comprises the steps of: providing a resinous solution by dissolving the siloxane-based resin in an organic solvent; coating a silicon wafer with the resinous solution; and heating the coated wafer to cure the resin.
According to the present invention, the resinous solution can further comprise a porogen, which is a pore-generating material. Non-limiting examples of the porogen useful in the present invention include cyclodextrin and derivatives thereof described in Korean Patent Appln. No. 2001-15883, as well as polycaprolactone and derivatives thereof described in U.S. Pat. No. 6,114,458. Preferred mixing ratio of the siloxane-based resin vs. porogen is between 99:1 and 30:70(w/w), more preferably 90:10 and 50:50(w/w).
Preferred organic solvents used in dissolution of the siloxane-based resin or a mixture of the siloxane-based resin and porogen to provide a resinous solution can be exemplified by, but are not limited to, aliphatic hydrocarbon solvents; aromatic hydrocarbon solvents such as anisole, mesitylene and xylene; ketone-based solvents such as methyl isobutyl ketone, 1-methyl-2-pyrrolidinone, cyclohexanone and acetone; ether-based solvents such as tetrahydrofuran and isopropyl ether; acetate-based solvents such as ethyl acetate, butyl acetate and propylene glycol methyl ether acetate; alcohol-based solvents such as isopropyl alcohol, butyl alcohol and octyl alcohol; amide-based solvents such as dimethylacetamide and dimethylformamide; silicon-based solvents; and mixtures thereof.
Upon preparing a resinous solution, the organic solvent should be used in a sufficient amount to apply the resin component evenly on the surface of a wafer. Thus, the organic solvent is added to the siloxane-based resin or to the mixture of the siloxane-based resin and porogen so that final concentration of the solid matter(inclusive of the siloxane-based resin and the porogen) is 0.1-80 wt %, preferably 5-40 wt %.
Non-limiting examples of the method for coating a silicon wafer with the resinous solution thus prepared include spin-coating, dip-coating, spray-coating, flow-coating, and screen-printing, while spin-coating is most preferred. For spin coating, the spin rate is controlled to be between 1,000 and 5,000 rpm.
After the coating, the organic solvent is evaporated from the wafer so that a resinous film comprising the siloxane-based resin can deposit on the wafer. At this time, the evaporation may be carried out by simple air-drying, or by subjecting the wafer, at the beginning of following curing step, to a vacuum condition or mild heating(xe2x89xa6100xc2x0 C.).
Subsequently, the resinous film is cured by heating for 1-150 min at a temperature of 150-600xc2x0 C., preferably 200-450xc2x0 C., so as to provide a insoluble, crack-free film. As used herein, by xe2x80x9ccrack-free filmxe2x80x9d is meant a film without any crack observed with an optical microscope at a magnification of 1000xc3x97. As used herein, by xe2x80x9cinsoluble filmxe2x80x9d is meant a film that is substantially insoluble in any solvent described as being useful for dissolving the siloxane-based resins.
The coating film thus formed was found to have dielectric constant below 3.0, preferably between 2.0 and 2.7, and so it is very useful as an insulating film between interconnect layers in semiconductor devices.
The present invention can be more clearly understood with referring to the following examples. It should be understood that the following examples are not intended to restrict the scope of the present invention in any manner.
To a flask were added 10.0 g(29.014 mmol) of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane and 0.164 g of platinum(O)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex(solution in xylene), and then diluted with 300 ml of diethylether. Next, the flask was cooled to xe2x88x9278xc2x0 C., 17.29 g(127.66 mmol) of trichlorosilane was slowly added thereto, and then it was slowly warmed to room temperature. The reaction was continued at room temperature for 20 hrs, and volatile materials were removed from the reaction mixture under a reduced pressure of about 0.1 Torr. To the mixture was added 100 ml of pentane and stirred for 1 hr, and then the mixture was filtered through celite. From the filtrate was evaporated pentane under a reduced pressure of about 0.1 Torr to afford a liquid compound represented by the following formula: 
10.0 g(11.28 mmol) of the liquid compound was diluted with 500 ml of tetrahydrofuran, and 13.83 g(136.71 mmol) of triethylamine was added thereto. Thereafter, the mixture was cooled to xe2x88x9278xc2x0 C., 4.38 g(136.71 mmol) of methyl alcohol was slowly added thereto, and then it was slowly warmed to room temperature. The reaction was continued at room temperature for 15 hrs and filtered through celite, and then volatile materials were evaporated from the filtrate under a reduced pressure of about 0.1 Torr. Subsequently, 100 ml of pentane was added to the filtrate and stirred for 1 hr, and then the mixture was filtered through celite to provide a clear colorless solution. Finally, pentane was evaporated from this solution under a reduced pressure of about 0.1 Torr to afford monomer (A) represented by the following formula: 
The results obtained from NMR analysis of monomer (A) dissolved in CDCl3 are as follows:
1H-NMR(300 MHz): xcex40.09(s, 12H, 4xc3x97xe2x80x94CH3), 0.52xcx9c0.64(m, 16H, 4xc3x97xe2x80x94CH2CH2xe2x80x94), 3.58(s, 36H, 4xc3x97xe2x80x94[OCH3]3)
To a flask were added 2.0 g(8.32 mmol) of 2,4,6,8-tetramethylcyclotetrasiloxane and 0.034 g of platinum(O)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex(solution in xylene), and then diluted with 100 ml of toluene, followed by addition of 7.75 g(33.36 mmol) of trimethoxy(7-octene-1-yl)silane. Next, the flask was slowly warmed to 75xc2x0 C. The reaction was continued at 75xc2x0 C. for 36 hrs, and then volatile materials were removed therefrom under a reduced pressure of about 0.1 Torr. To the reaction mixture was added 100 ml of pentane and stirred for 1 hr, and then the mixture was filtered through celite. Subsequently, pentane was evaporated from the filtrate under a reduced pressure of about 0.1 Torr to afford monomer (B) represented by the following formula: 
The results obtained from NMR analysis of monomer (B) dissolved in CDCl3 are as follows:
1H-NMR(300 MHz): xcex40.11(s, 12H, 4xc3x97xe2x80x94CH3), 0.48xcx9c0.53(m, 8H, 4xc3x97xe2x80x94CH2xe2x80x94), 0.86xcx9c0.90(m, 8H, 4xc3x97xe2x80x94CH2xe2x80x94), 1.15xcx9c1.71(m, 48H, 4xc3x97xe2x80x94[CH2]6), 3.58(s, 36H, 4xc3x97xe2x80x94[OCH3]3)
To a flask was added 10.0 g(7.194 mmol) of octa(chlorosilylethyl)-POSS[Polyhedral Oligomeric Silsesquioxane] and diluted with 500 ml of tetrahydrofuran, followed by addition of 6.41 g(63.310 mmol) of triethylamine. Next, the flask was cooled to xe2x88x9278xc2x0 C., and 2.03 g(63.310 mmol) of methyl alcohol was slowly added thereto, and then it was slowly warmed to room temperature. The reaction was continued at room temperature for 20 hrs, filtered through celite, and then volatile materials were evaporated from the filtrate under a reduced pressure of about 0.1 Torr. Subsequently, 100 ml of pentane was added to the filtrate and stirred for 1 hr, and then the mixture was filtered through celite to provide a clear colorless solution. Finally, pentane was evaporated from this solution under a reduced pressure of about 0.1 Torr to afford monomer (C) represented by the following formula: 
The results obtained from NMR analysis of monomer (C) dissolved in CDCl3 are as follows:
1H-NMR(300MHz): xcex40.11(s, 48H, 8xc3x97xe2x80x94[CH3]2), 0.54xcx9c0.68(m, 32H, 8xc3x97xe2x80x94CH2CH2xe2x80x94), 3.43(s, 24H, 8xc3x97xe2x80x94OCH3)
To a flask was added 10.0 g(6.438 mmol) of octa(dichlorosilylethyl)-POSS and diluted with 500 ml of tetrahydrofuran, followed by addition of 11.47 g(113.306 mmol) of triethylamine. Next, the flask was cooled to xe2x88x9278xc2x0 C., and 3.""g( 113.306 mmol) of methyl alcohol was slowly added thereto, and then it was slowly warmed to room temperature. The reaction was continued at room temperature for 20 hrs, filtered through celite, and then volatile materials were evaporated from the filtrate under a reduced pressure of about 0.1 Torr. Subsequently, 100 ml of pentane was added to the filtrate and stirred for 1 hr, and then the mixture was filtered through celite to provide a clear colorless solution. Finally, pentane was evaporated from this solution under a reduced pressure of about 0.1 Torr to afford monomer (D) represented by the following formula: 
The results obtained from NMR analysis of monomer (D) dissolved in CDCl3 are as follows:
1H-NMR(300 MHz): xcex40.12(s, 24H, 8xc3x97xe2x80x94CH3), 0.56xcx9c0.70(m, 32H, 8xc3x97xe2x80x94CH2CH2xe2x80x94), 3.46(s, 48H, 8xc3x97xe2x80x94[OCH3]2)
To a flask was added 5.0 g(2.913 mmol) of octa(trichlorosilylethyl)-POSS and diluted with 500 ml of tetrahydrofuran, followed by addition of 7.78 g(76.893 mmol) of triethylamine. Next, the flask was cooled to xe2x88x9278xc2x0 C., and 2.464 g(76.893 mmol) of methyl alcohol was slowly added thereto, and then it was slowly warmed to room temperature. The reaction was continued at room temperature for 20 hrs, filtered through celite, and then volatile materials were evaporated from the filtrate under a reduced pressure of about 0.1 Torr. Subsequently, 100 ml of pentane was added to the filtrate and stirred for 1 hr, and then the mixture was filtered through celite to provide a clear colorless solution. Finally, pentane was evaporated from this solution under a reduced pressure of about 0.1 Torr to afford monomer (E) represented by the following formula: 
The results obtained from NMR analysis of monomer (E) dissolved in CDCl3 are as follows:
1H-NMR(300 MHz): xcex40.66xcx9c0.69(m, 32H, 8xc3x97xe2x80x94CH2CH2xe2x80x94), 3.58(s, 72H, 8xc3x97xe2x80x94[OCH3]3)